The term "superconductivity" is applied to the phenomenon of immeasurably low electrical resistance exhibited by materials. Until recently superconductivity had been reproducibly demonstrated only at temperatures near absolute zero. As a material capable of exhibiting superconductivity is cooled, a temperature is reached at which resistivity begins to decrease (conductivity begins to increase) markedly as a function of further decrease in temperature. This is referred to as the superconducting onset transition temperature or, in the context of superconductivity investigations, simply as the onset critical temperature (T.sub.c). T.sub.c provides a conveniently identified and generally accepted reference point for marking the onset of superconductivity and providing temperature rankings of superconductivity in differing materials. The highest temperature at which superconductivity (i.e., zero resistance) can be measured in a material is referred to as the onset superconductivity temperature (T.sub.o).
H. Maeda, Y. Tanaka, M. Fukutomi, and Y. Asano, "A New High T.sub.c Superconductor Without a Rare Earth Element", Japanese Journal of Applied Physics, Vol. 27, No. 2, pp. L209 and L210, first reported that at least one compound of bismuth, strontium, calcium, copper, and oxygen had been found to be super-conducting.
One of the difficulties that has arisen in attempting to form films of bismuth mixed alkaline earth copper oxides that are superconducting is that high sintering temperatures are required to form the crystalline grains of bismuth mixed alkaline earth copper oxide responsible for superconductivity. It is the necessity of sintering at high temperatures that has set the formation of superconducting films in a class apart from the preparation of bulk superconducting materials. In conductive film fabrication substrate interaction with the film during sintering must be taken into account. The greater the thermal driving force (a function of the time and temperature of sintering) required to form the crystalline grains of the film, the greater is the risk of degradation due to unwanted interaction between the conductive film and substrate.
S. Jin et al, Appl. Phys. Lett. 52(19), 9 May 1988, pp. 1628-1630, reports the incorporation of silver in bismuth strontium calcium copper oxides.